Looking on the internet deeply has found these results:

there is a myriad of reasons is the most popular phrase on the web.

there are a myriad of reasons 1509,000 results on the web	there is a myriad of reasons 11,520,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
There are a myriad of texts from his wife wondering why he is late for a flight to Chicago an hour ago. And I have not survived a myriad of diseases and natural disasters. There were a myriad of problems which conspired to corrupt your reason and rob you of your common sense. There are a myriad of contributory factors There are a myriad of differences, believe me. fewer smallholdings, deforestation, desertification, lack of access to water and climate change. A myriad of different interests are involved within the industry. A myriad of apologies, sir.	And I have not survived a myriad of diseases and natural disasters. There are a myriad of differences, believe me. A myriad of different interests are involved within the industry. This could backfire in a myriad of ways. A myriad of apologies, sir. There were a myriad of problems which conspired to corrupt your reason and rob you of your common sense. There were a myriad of problems which conspired...

there are a myriad of reasons

1509,000 results on the web

there is a myriad of reasons

11,520,000 results on the web

More popular!

There are a myriad of texts from his wife wondering why he is late for a flight to Chicago an hour ago.
And I have not survived a myriad of diseases and natural disasters.
There were a myriad of problems which conspired to corrupt your reason and rob you of your common sense.
There are a myriad of contributory factors
There are a myriad of differences, believe me.
fewer smallholdings, deforestation, desertification, lack of access to water and climate change.
A myriad of different interests are involved within the industry.
A myriad of apologies, sir.

And I have not survived a myriad of diseases and natural disasters.
There are a myriad of differences, believe me.
A myriad of different interests are involved within the industry.
This could backfire in a myriad of ways.
A myriad of apologies, sir.
There were a myriad of problems which conspired to corrupt your reason and rob you of your common sense.
There were a myriad of problems which conspired...